$http does not remove headers when functional config value returns null

[perek]

From AngularJs docs (http://docs.angularjs.org/api/ng.$http#usage):

headers – {Object} – Map of strings or functions which return strings representing HTTP headers to send to the server. 
If the return value of a function is null, the header will not be sent.

This can be reproduced via these lines in an app in 1.2.x:

$http.defaults.headers.common.Authorization = 'Basic';
$http({method:'GET',headers: { 'Authorization': function(){return null;}}, url: '/url'});

This code should not send a an Authorization header, but it does as of 1.2.x

[clakech]

👍 I confirm this issue here with 1.2.8